> Does this mean that for now and the near future, with Linux/Qt/KDE,
>
> - no one can use the non-BMP private use area

Precisely. Unless "there is serious user demand for it", as I wrote.

> - new assignments and fonts for them cannot be prototyped for

Not in other planes, with our code. There's just so much we can do,
and that's one of the things that's so far down on the list that I
personally don't think it will get to the top.

> - the language tags in plane 14 that the Internet Mail Consortium proposes
> to use (prematurely I know since they are not really standard yet) cannot
> be used

Indeed.

> What is missing?

Time and testing, mostly. Supporting things takes time. We provide
what application developers need, and implementing something that
people aren't asking for and which we cannot test must obviously be
far down on the list of priorities.